The objective of this work is to characterize the microscopic kinetics of the excitable tissues of nerve and muscle through the use of both electrical and optical measurements. These experiments will provide quantitative data on the conducting states of the sodium and potassium systems of the excitable membranes of both nerve and muscle. The muscle studies will be extended to identification of contractile unit events as well as kinetic information on myofilament motion. Optical diffraction measurements will be quantitatively compared with known theory and used to develop a more complete description of structure during muscle contraction.